Caster assembly and shelf system for use on a collapsible cart

ABSTRACT

Disclosed is a lightweight caster assembly and modular shelf system for use on an existing collapsible foldable cart with four wheels.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to the field of material handling andcarts.

2. Description of Prior Art

Many improvements have been made in the field of carts and dollies. Thepresent inventor, Dahl, in U.S. Pat. No. 5,228,716, teaches a cart withfoldable sides and a telescoping frame adapted to accommodate numerousshapes and sizes of cargo. Dahl's first carts utilized relatively smalldiameter swivel casters with solid wheels that were problematic forusers who needed to traverse grass or dirt, particularly with heavyloads. Many professional film crews and sound crews require carts thatwould feature 4 pneumatic wheels to roll heavy equipment over roughterrain, such as grass football fields, that nonetheless will fold to asmall storage size for easy transport in SUVs or airlines. Because allknown 4-wheeled carts featuring pneumatic wheels are extremely heavy andbulky, they are not functional in terms of folding to a small storagesize for use in smaller vehicles or airlines, where sheer bulk of thecarts displace valuable space needed for equipment storage. Furthermore,airlines have recently raised rates for extra cargo, making lower weightand size of traveling equipment crucial. In addition to the need ofpneumatic wheel units mounted on a foldable cart, video and sound crewsoften require a shelf that would attach quickly to the cart in the fieldin order to support camera, video, or sound equipment. The inventor setabout creating a collapsible cart and expandable shelf system that wouldremedy these concerns.

Others have realized the usefulness of pneumatic wheels on carts,however, they have failed to solve the problems of weight,transportability, or to effectively eliminate caster “shudder” or“chatter” while a cart is rolling. U.S. Pat. No. 3,785,669 to Dohenyteaches a convertible cart that is often used by video professionals whohave sometimes replaced the original 5″ swivel casters with pneumaticswivel casters. However, this cart is extremely heavy, bulky, and doesnot fold down with the pneumatic casters attached. In addition, theframe fails to retract in length making the storage size unsuitable forSUV's, etc. U.S. Pat. No. 4,009,891 teaches a convertible cart that doesnot fold small for storage, is extremely heavy, and does not featurepneumatic casters which would require extensive redesigning of theframe. Regarding technology relating to a cart shelf to support camera,video or sound equipment, others have attempted such an improvement, buthave not done so in a manner that teaches the limitations of the presentinvention. For instance, U.S. Pat. No. 5,536,034 to Miller teaches aconvertible bulk hand truck and tabletop, however, this is essentially atable mounted to Doheny's cart. Unfortunately, the Miller technology asconfigured was too bulky and heavy when transporting in a vehicle orairline. The present invention is materially different in form andfunction. Other wheeled devices and table combinations are shown in U.S.Pat. Nos. 4,284,286, 4,565,382, 5,004,263; 5,160,182; 5,201,536,however, none of these patents have configurations and functionalcapability of serving as a two wheeled dolly and four wheeled cart whilealso including features that serve to convert the four wheeled cart intoa portable work table.

Because of the substantial demands of film and video crews for extremelycollapsible carts to carry extremely heavy loads over rough terrain, thepresent invention typically employs four 8-10″ diameter pneumatic wheelunits on the inventor's collapsible cart. Although such pneumatic wheelunits are naturally lighter than solid tire counterparts, the inherentdiameter of the wheel still presents a significant challenge in terms ofportability and weight. These factors contributed to the genesis of theinvention of this cart model. Obstacles included but were not limited tooversized and excessively heavy mounting plates on commerciallyavailable caster and wheel units that could not be utilized withoutsignificantly interfering with the functionality of the cart. Typicalpneumatic plate casters were far too heavy (exceeding 7-8 pounds each),which when used in the inventor's 2-wheel handtruck configuration causedthe inventor's previous carts to become top-heavy and topple over. Theframe design used by the inventor on the entire frame design weighedless than 25 pounds without the casters, so this excessive weight wasunacceptable. U.S. Pat. No. 3,283,358 to Merriam teaches such a commonplate caster, however, this design is extremely heavy, and tended tointerfere with the operation of the inventor's cart. Typical platecasters with pneumatic wheels were not usable because the width of themounting plates (typically 4″×4.5″ diameter) would strike against theframe components and interfere with the folding handle operation of thecart. In addition, mounting the steel plate to the square tube frontaxel of the inventor's cart was cumbersome, heavy, bulky, and negatedmany of the design goals of the inventor. The bulky caster mountingplate would constantly snag on items during storage/transport and wouldrequire significant widening of the front axel, a feature furtherdiscussed herein. During the inventive process, and in researchingavailable caster and wheel technologies, the inventor found thatexisting units featured bulky bearing caps that would interfere withoperation and the release mechanisms of the foldable handles. Althoughpneumatic stem (post) casters are available, they too were also foundtoo heavy and bulky to allow the inventor's cart to function correctly.Because of weight, they also would cause the cart to topple over whenused in upright 2-wheel handtruck position (one of the inventor's cart'sfoldable positions). For instance, U.S. Pat. No. 4,709,444 to Blackteaches a stem caster wheel unit secured by pins, but this caster is notremovable and the stem is solid which added too much weight. Inaddition, the horn assembly of Black weighted too much if enlarged toaccommodate an 8″ diameter pneumatic wheel. U.S. Pat. No. 164,226 toSheldon teaches a stem furniture caster that has no way of securing thestem inside the furniture to accommodate constant removal and if thearticle was to be constantly lifted off of the ground. Similarly, U.S.Pat. No. 4,969,230 to Huang and U.S. Pat. No. 4,707,880 to Doyle teachremovable stem casters, however the solid stem was also determined tooheavy for application with inventor's cart. U.S. Pat. No. 4,224,714 toSalpos discloses a caster essentially designed for use with woodfurniture, which is unsuitable. U.S. Pat. No. 6,810,561 to Liu teaches aring stem caster with a threaded bolt that would be far too heavy whenenlarged to accommodate 8″ diameter pneumatic tires. For these reasons,the inventor developed a novel wheel and caster unit with a smallbearing cap and modified tube stem extending therefrom.

Another major problem addressed by this invention is that pneumaticswivel casters tend to shudder excessively when mounted on a cart with alightweight frame. This “chatter” or “shudder” (side-to-side wobbling)is very undesirable when transporting delicate and expensive photo,video, or musical equipment (or any other cargo) and greatly reduces thecart's functionality. This problem is also compounded because largerubber pneumatic tires have a tendency while rolling to stick slightlyor grab on hard surfaces such as concrete. The lighter the cart frame,the more pronounced are such problems. The combination of the inventor'slightweight frame (approximately 25 lb.) and the large diameter of thepneumatic casters (8-10″ diameter), created excessive caster chatterwhen installed on inventor's cart frame. This chatter would renderinventor's cart unusable as a viable equipment mover. The inventorattempted to solve the problem with commercially availabletechnologies—to no avail. U.S. Pat. No. 5,809,612 to Finch teaches ananti-shimmying caster wheel, however, it is functionally different thanthis inventor's solution. Finch's technology was also heavy and not aneconomically viable alternative for use with the present invention. U.S.Pat. No. 4,097,954 to Christiansen teaches a flutter-resistant casterthat would cause premature bearing wear when used with a casterfeaturing 8″ or larger diameter wheels and heavy loads. In addition, theplate mount was undesirable because of weight and bulk.

In addition, inventor's frame needed to be significantly redesigned toaccommodate this caster and still meet the original design goals of thecart in terms of small storage size, expandable frame, stability andsteady transport. Early in the design process, research determined thatthe cart would topple over when making sharp turns with pneumaticcasters installed in the same position as smaller casters on previouscarts. To maintain turn stability and maintain a small storage size,further research revealed a preferable width of a front axle on theframe of the cart of at least eighteen inches in width. The inventor'scart had the front axel modified accordingly to accommodate this newtype of caster and to prevent toppling of the cart when the cart madesharp turns. The pneumatic swivel casters were therefore positionedfarther apart on the front axel than the smaller casters on previouscarts.

To further transform inventor's cart into a field workstation whilemeeting Dahl's original design goals, a new type of shelf system wasdesigned which featured light weight, fast set-up, and small storagesize for transport when removed from the cart. In addition, this shelfcould change length that could be mirrored by altering the length of theinventor's telescoping cart. This feature is extremely advantageous insituations when space was at a premium in the field, using a smallequipment set-up, or navigating the labyrinth hallways in auditoriums,hotels, etc. The shelf was attached to the cart via holes in thefoldable handles and using wingbolts and wingnuts. U-shaped bracketswelded to the steel shelf support tubes fit over the vertical carthandles providing a rigid shelf platform when the wingbolts weretightened.

SUMMARY OF THE INVENTION

Accordingly, to meet the inventor's original design goals andaccommodate inventor's cart frame, it is a primary object of the presentinvention to provide a new type of pneumatic caster and mounting systemfeaturing preferences including nominal weight, structural strength,economical manufacturing costs, a wheel chatter dampener, a slimmerprofile than typical pneumatic casters, a preferable expandable shelfattachment, and a new method of attaching the foregoing to the frame tofunction with inventor's collapsible cart.

It is the object of this invention to design a cart featuring anexpandable frame, foldable sides, that transforms into at least threeconfigurations, will accommodate two pneumatic rear wheels, twopneumatic caster wheel units, fold down to a small storage size fortransport, and accommodate a shelf system that attaches/detaches quicklyin the field.

It is an object of this invention to design a cart featuring an axlewith strategically positioned holes drilled in the front axle, therebyreducing the front axle weight, maintain structural strength, provide anarea where bungee cords can be mounted, and improve the weight balanceratio of the cart frame such that the cart could function as a 2-wheelhand truck without toppling over when pneumatic casters installed onsaid cart frame.

It is an object of this invention to provide a lightweight pneumaticcaster that will allow inventor's cart frame to function inconfigurations similar to those with 5″ wheel diameter or smallercasters.

It is the object of this invention to design to provide a pneumaticcaster that is approximately 40% lighter than typical pneumatic casters,and which will allow inventor's cart to function as a two-wheelhandtruck and fold to a small storage size.

It is the object of this invention to feature a caster with polymer hubsso as to significantly reduce the weight of steel hubs.

It is the object of this invention to provide a pneumatic casterfeaturing a tube axle with retaining cotter pins, or similar means, toreduce weight and eliminate typical heavy bolt axles with nuts.

It is the object of this invention to provide a pneumatic casterfeaturing a tube axle with retaining cotter pins so as to facilitateextremely fast tire replacement in the field with a bare minimum oftools.

It is the object of this invention to provide a pneumatic caster that isinexpensive to manufacture.

It is the object of this invention to provide a pneumatic casterfeaturing a specially machined vertical tube stem that is structurallystrong, yet lightweight, so as to attach the caster to the cart frontaxle. In addition, this stem must be designed such that the stem couldbe swaged from below the bearing races in order to secure the stem,bearing races, and yoke as one assembly.

It is the object of this invention to provide a pneumatic casterfeaturing strategically positioned holes in the caster horn to reduceweight yet maintain structural strength.

It is the object of this invention to provide a pneumatic casterfeaturing a horn composed of thinner wall steel than similar sizecasters so as to significantly reduce the weight of the overall caster.

It is the object of this invention to provide a pneumatic casterfeaturing lightweight roller bearings surrounding the tube axle toeliminate heavier ball bearing casings.

It is the object of this invention to provide a pneumatic casterfeaturing at least one aperture drilled in each stem so as to facilitatea pin, preferably clevis or cotter, for easy removal or replacement inthe field, thereby eliminating the need for a large, heavy nut requiredby a solid threaded stem. Furthermore, such pin can be instantly pulledand the wheel removed so as to render that cart even smaller fortransport if necessary.

It is the object of this invention to provide a pneumatic casterfeaturing a chatter dampener comprising an oversized elastomeric O-ringwhich hugs the outside of the bearing cap—situated in the gap betweenthe upper and lower bearing caps—yet with just enough resistance toprevent chatter and yet allow the caster wheel to freely swivel

It is the object of this invention to provide a shelf system that willquickly and easily attach and detach from inventor's cart in the fieldwithout special tools.

It is the object of this invention to provide a shelf system that willhave structural integrity yet break down to a small size for storage andtransport, and which will easily attach to inventor's cart.

It is the object of this invention to provide a shelf system that mayvary in length so as to accommodate different field environment needs aswell as the expandable frame of inventor's cart.

These and other objects, advantages, and features of the presentinvention will become more apparent from the following detaileddescription when taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The manner in which these objectives and other desirable characteristicscan be obtained is explained in the following description and attacheddrawings in which:

FIG. 1 is a side perspective view of the disclosed caster unit.

FIG. 2 is a side perspective view of the collapsible, foldable cartfeaturing the disclosed caster unit of FIG. 1 and a new shelf system.

FIG. 3 is a side perspective view of the cart of the present inventionin a truncated form with the shelf unit.

FIG. 4 is a side perspective view of the inventor's cart featuring thecaster unit, but without the shelf unit.

FIG. 5 is a bottom perspective view of the two piece shelf-system of thepresent invention that shows how the frames of the respective pieces areadapted to connect to one another to form an extended shelf when thetelescoping cart is in extended form.

FIG. 6 is a side perspective view demonstrating how the caster unit ofthe present invention is adapted to fit into the cart frame where it issecured.

FIG. 7 is a close-up perspective top view of a preferable connectingmeans for securing the shelf to the handle of the cart.

FIG. 8 is a bottom perspective view of two respective components of themodular shelf system which can be fastened together and used as a singleelongated shelf, or where one of the respective shelf units may be usedin conjunction with the bracket inserts to form a truncated shelf foruse with the cart.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a side perspective view of the caster unit 1 disclosed in thepresent application. The caster unit 1 features a pneumatic tire 2 witha lightweight hub 3 disposed centrally within the pneumatic tire 2. Thehub 3 is preferably of polymer construction, although lightweightaluminum, lightweight alloys, ceramics and composite materials are alsocontemplated. Rather than a solid axle as found on other commercialcasters, the caster unit 1 features a hollow tube axle 4 that extendsthrough a central channel of the hub 3. The hollow tube axle 4 extendsthrough said hub 3 and extends on opposite sides of said hub 3 andconnects to a horn 5 of the caster unit 1. The horn 5 has a first side 6and second side 7 and forms a fork over and around hub 3 and tire 2. Thehorn sides (6 and 7) receive the hollow tube axle 4 through axlereceiving apertures 8 disposed on a lower portion of the horn sides (6and 7). The hollow tube axle 4 is securely fixed to the respective hornsides (6 and 7) through use of a securing means 9, which is preferably acotter pin that extends through a plurality of holes drilled at the endsof the hollow tube axle 4 that protrudes through the horn side (6 and7). The use of a hollow tube axle 4 is an important feature of thepresent invention because of the reduction in weight it affords. Apreferable diameter of such a hollow tube axle 4 is in the range of 15to 20 millimeters. The securing means 9 in the preferable form of acotter pin is also beneficial for purposes of weight and bulk reduction.For similar reasons of weight reduction, the inventor has punched aplurality of horn holes 10 in each of the horn sides (6 and 7). Thesteel used to construct horn 5 is preferably of ⅛-inch thickness. Theinventor contemplates that other materials may be used for horn 5, forinstance, aluminum, alloys, and composites. The horn sides (6 and 7)extend upward where they fuse to the underside of a bearing retainerunit 11.

The bearing retainer unit 11 of the present invention shares certainfeatures commonplace to most commercially available double ball racecasters. It is generally known in the caster industry that double raceswivel casters have two rows of ball bearings moving independentlythrough two levels of ball races. In all double race swivel casters,retainers encapsulate the rows of ball bearings, with bearings andretainers held together by a centrally fixed stem or bolt extendingtherethrough, but which securing of components does not restrict theswivel action of the caster or caster horn fixed to a wheel unit. Singlebearing race casters can operate as a bearing retainer unit 11 for thisinvention, however, it is preferable to use double ball race casters.The top ends of commercially swivel casters are further typicallydefined by either a “stem” or a mounting “plate,” both of which areadapted to attach to whatever object is in need of a caster. The bearingretainer unit 11 of the present invention is preferably comprised of alower retainer 12, on which sit the lower bearings 13. The lowerbearings 13 are a plurality of ball bearings that form a ring forpurposes of swivel function and load bearing. The lower bearings 13 arebound from above by the bottom surface of an upper retainer 14. On thetop surface of upper retainer 14 rest upper bearings 15, which are alsoa plurality of ball bearings that form a ring for purposes of swivelfunction and load bearing. A bearing cap 16 contains the upper bearings15 from above. A tube stem 17 defines the top of the inventor's bearingretainer unit 11 and extends centrally through the bearing cap 16, upper14 and lower 12 retainers which encapsulate upper 15 and lower 13bearings. The inventor's bearing retainer unit 11 is preferably heldtogether as one assembly by “swaging.” It should also be noted that theinventor's bearing cap 16 is notably smaller than most commerciallyavailable casters, preferably rounded, and formed of lightweightindustrial materials, for instance, thin steel or aluminum. As with mostcommercially available casters, the inventor's first 6 and second 7 hornsides connect rigidly to the bearing retainer unit 11 preferably at theunderside of the upper retainer 14. The horn unit 5 and upper retainer14 may be preferably formed as a single forged or cast unit.

Important distinguishing features of this invention include a tube stem17 with an upper exposed portion (portion above the bearing cap 16) ofthe tube stem 17 being partially hollow. Up to eighty (0-80%) of theexposed portion of the tube stem 17 may be hollow. This hollowed tubestem 17 may be accomplished by a variety of means, including but notlimited to casting, machining, molding, etc. The hollowed stemcontributes to the overall lessening of cart weight; and because it isnot completely hollow, it will have enhanced strength where needed atits base. It is expected that those skilled in the art will appreciatethe utility of this feature for applications other than the inventor'scart. Also, it should be noted that because the lower exposed portion ofthe tube stem 17 is not hollow, it is capable of supporting the“swaging” action used to compress and secure the bearings, retainers andbearing cap assembly.

Also disposed along the hollow portion of the tube stem 17 are at leastone, and preferably two oppositely situated tube stem apertures 18. Tubestem apertures 18 permit securing of the caster unit 1 to any item towhich the caster unit 1 needs to be secured, such as the inventor'scart, by securing means that extend through the tube stem apertures 18.A preferable stem securing means is a clevis pin, particularly sinceeasy separation of the caster unit 1 from the object to which it isattached (such as a cart) is desirable for purposes of transportability.Other stem securing means may be used that accomplish the purpose ofsecuring the caster to an item, for instance a cart, but the clevis pinhas been found most suitable for the inventor's purposes. A cotter pin,a combination clevis pin with ball-and-detent mechanism, rapid releaseremovable pins, or even a screw and bolt apparatus will also be typicalpreferable tube stem securing means.

A major problem with prior art casters solved by the present inventionis the “chatter” or “shudder” (rapid side-to-side motion) of casterswhile rolling. The chatter problem is further compounded when a casteris attached to a light frame, such as the inventor's cart. The inventorhas solved this problem through use of a chatter dampener 19. Thischatter dampener 19 is fixed along the periphery and between the upperbearing cap 16 and upper retainer 14 of the bearing retainer unit 11.These are the terms used for the inventor's disclosure; however, thecritical location for use of a chatter dampener 19 is along theperiphery and just between the swivel unit and the upper stationaryunit, which in the inventor's caster unit 1 is described as the upperretainer 14 and respective bearing cap 16. The chatter dampener 19operates by slightly checking and adding resistance to the swivel motionof the caster unit 1. Preferably, the chatter dampener 19 is anelastomeric ring, or an O-ring, that hugs the outside of the gap that isfound around the periphery and between the bearing cap 16 and upperretainer 14. The chatter dampener 19 is of a diameter just large enoughso that it does not retract into the gap found around the peripherywhere it would unduly interfere with swivel function. Rather, thechatter dampener 19 slightly protrudes from the gap to dampen the swiveland corresponding “chatter” motion. The chatter dampener 19 is typicallyinstalled by the method of pulling it over the stem side of the casterunit 1 and affixing the same securely along the outside of the gapspanning between the bearing cap 16 and upper retainer 14. The inventorcontemplates that a variety of materials could be used to form thechatter dampener 19, including but not limited to rubber, silicon,plastic, or composite materials.

The caster unit 1 of the present invention weighs in the range of 3 to 5pounds when fitted with an 8-inch pneumatic tire (2.50-4). This iscompared to a typical commercially available caster unit weighing 7.9pounds. The weight of the inventor's caster unit 1 is, therefore, in therange of thirty (30%) to fifty (50%) lighter than comparabletechnologies. Considering that four wheels are commonly used on manycarts, this could easily reduce weight by thirteen (13) pounds.

To further enhance the utility of the present cart, the inventordeveloped a modular shelf system that expands consistent with thecollapsible or telescoping feature of the inventor's existing carts. Ascan be seen in FIG. 2 (expanded cart) and FIGS. 3 and 4 (truncatedcart), the inventor's cart has a telescoping frame 20 that increases ordecreases in length, depending on the user's needs, and which frame isthen secured with an extension stop pin mechanism and as well by manualtwisting of a spring assisted bolt. This basic function is disclosed ininventor Dahl's previous U.S. Pat. Nos. 5,228,716 and 5,476,282. Alsoshown are the handles 21 on opposite sides of the telescoping frame 20,which are foldable down flush with the telescoping frame 20. Thus, basicfunctionalities of the existing invention were a foldable, collapsiblecart with four wheels. The inventor now discloses a shelf system 22 thataccommodates the telescoping feature of the cart. The shelf system 22comprises a first shelf unit 23 and a second shelf unit 24. If firstshelf unit 23 and second shelf unit 24 are fixed to one another, theypreferably extend to fit the length of the cart in extended telescopingmode, which is typically and preferably approximately 53 inches inlength. If a truncated cart and shelf is desired, the system is adaptedso that the user of the cart will modify the second shelf unit 24 sothat it fits between and fixes to opposite handles 21 of the cart. Intruncated form, the shelf is typically and preferably approximately 29inches in length. Shelves are adapted to connect at furthest ends of theshelves to the handles 21 located on opposite ends of the cart. As shownin FIGS. 2, 3, 4 and close-up FIG. 7, shelves attach to handles 21 atthe point of handle apertures 25, a plurality of which are preferablylocated along the length of the handles 21. Multiple sets of handleapertures 25 may be located along the length of the handles 21 toaccommodate a plurality of shelf units, or to accommodate alternateplacement choices for one shelf on the length of the handles 21 of thecart. As shown in FIGS. 2, 3, 4 and 7, a connector means 26 is used tofix the shelf ends to the handles 21. A preferable connector means 26 isin the form of a U-bracket extending from and disposed at the ends ofthe shelf frame 27. U-brackets are preferable for the present inventionbecause they fit snugly around the cart handles 21 which are preferablymade from square tube steel. U-brackets are preferably fixed in place bya pin mechanism extending through bracket holes 28 in the U-bracket andthe handles 21 of the cart. Pin mechanisms commonly suitable would becoffer pins, clevis pins, ball and detent pins, bolt and wingnuts, etc.As shown in FIGS. 5 and 8, both first shelf unit 23 and second shelfunit 24 are supported by a shelf frame 27 that is comprised of solidsupports, preferably square tube steel or aluminum, running the lengthof the respective shelf units. This invention employs at least two solidsupports of preferable tube steel that also preferably are fixed to theunderside of the first (23) and second (24) shelf units. Tube steel isparticularly preferable for solid supports comprising the shelf frame27. Also, it is preferable that the shelf frame 27 of the first shelfunit 23 be formed from tube steel smaller than the tube steel used onthe shelf frame 27 of the second shelf unit 24, thereby allowing thesmaller tube steel frame to insert inside the larger tube steel framewhen the respective shelf units are connected to one another. It ispreferable to use twenty-five millimeter square tube steel on the secondshelf units 24 and twenty-millimeter square tube steel on the firstshelf unit 23. The main body of the shelf units is made of materialsthat are strong and lightweight, for instance, light wood, plastic,aluminum, composite materials, etc., and they may also be covered by aresilient felt or fabric material typical for use with sound equipment.The first (23) and second (24) shelf units are adapted to connect to oneanother by a unit connector 29 at facing ends. The unit connector 29 ispreferably formed of male ends defining frame ends of a shelf unit thatinserts into female receivers on the frame ends of a connecting shelfunit. Thereafter, the unit connector 29 is further secured and tighteneddown by use of preferable extension stop pins and spring-loadedwingbolts. This is usually accomplished by having the square tube steelof the shelf frame 27 of one of the respective shelf units smaller thanthe square tube steel of the shelf frame 27 of opposite connecting shelfunit. Preferably the male end is from tube steel and is located on theends of shelf frame 27 of the first shelf unit 23. The female receiversare disposed on accommodating shelf frame 27 ends of the second shelfunit 24. If the user chooses to use a truncated cart form, andrespective truncated shelf fixture, the user must modify the shelf unit,preferably the second shelf unit 24, by installing bracket inserts 30into the shelf frame 27 at the point where unit connectors 29 wouldtypically receive the male ends of the shelf frame 27 of the first shelfunit 23 (in extended shelf mode). Such bracket inserts 30 when securelyfixed allow both ends of second shelf unit 24 to connect to the handles21 of the folding cart. Bracket inserts 30 are preferably U-bracketsthat face in the same direction as the connectors on opposite end of thesecond shelf unit 24.

The present invention has been illustrated in great detail by the abovereferenced examples, however, it is to be understood that such examplesare illustrative and that this invention is not limited by any of thedetails in the illustrations. Those skilled in the art will understandthe present invention is capable of many variations without deviatingfrom the scope of the invention. Accordingly, the claims are to beconstrued broadly within the scope of the invention.

1. A cart caster unit comprising: (a) a pneumatic tire featuring a hubfixed to and disposed within said tire; (b) a hollow tube axle extendingthrough a central channel of said hub, said tube axle connecting to ahorn by securing means at opposite ends of said hollow tube axle; (c)said horn connecting to the underside of a bearing retainer unit, saidbearing retainer unit having an upper bearing cap; (d) where a tube stemextends through said bearing retainer unit, (e) wherein said tube stemis defined by a solid lower base portion adjacent the upper bearing cap,and a tubularly hollow, upper portion the solid lower base portion beingsolid throughout a cross-section thereof; (f) wherein the tubularlyhollow upper portion defines up to 80% of said exposed portion of antube stem, said exposed portion of the tube stem being the portion ofsaid tube stem disposed above said upper bearing cap; and, (g) whereinthe entire caster unit is in the range of 3 to 5 pounds.
 2. The cartcaster unit of claim 1 wherein the securing means is a cotter pin. 3.The cart caster unit of claim 1 wherein said horn is formed from ⅛ inchsteel.
 4. The cart caster unit of claim 1 wherein said horn has aplurality of horn holes, whereby the caster unit weight is reduced. 5.The cart caster unit of claim 1 wherein the hub is formed from a polymerplastic.
 6. The cart caster unit of claim 1 wherein said hollow tubeaxle is of a diameter in the range of 15 to 20 millimeters.
 7. The cartcaster unit of claim 1 wherein said tube stem features at least one tubestem aperture adapted to receive a stem securing means, whereby thecaster unit is selectively removable.
 8. The cart caster unit of claim 1wherein said pneumatic tire is in the range of 8 to 10 inches.
 9. Thecart caster unit of claim 1 wherein said bearing retainer unit featuresa chatter dampener disposed along the periphery of said bearing retainerunit between the upper bearing cap and an upper retainer of said bearingretainer unit, and whereby caster unit chatter is reduced.
 10. The cartcaster unit of claim 9 wherein said chatter dampener is an elastomericO-ring.